Indirect additive manufacturing(AM)methods have recently attracted attention from researchers thanks to their great potential for cheap,straightforward,and small-scale production of metallic components.Atomic diffusio...Indirect additive manufacturing(AM)methods have recently attracted attention from researchers thanks to their great potential for cheap,straightforward,and small-scale production of metallic components.Atomic diffusion additive manufacturing(ADAM),a variant of indirect AM methods,is a layer-wise indirect AM process recently developed based on fused deposition modeling and metal injection molding.However,there is still limited knowledge of the process conditions and material properties fabricated through this process,where sintering plays a crucial role in the final consolidation of parts.Therefore,this research,for the first time,systematically investigates the impact of various sintering conditions on the shrinkage,relative density,microstructure,and hardness of the 17-4PH ADAM samples.For this reason,as-washed samples were sintered under different time-temperature combinations.The sample density was evaluated using Archimedes,computed tomography,and image analysis methods.The outcomes revealed that sintering variables significantly impacted the density of brown 17-4PH Stainless Steel samples.The results indicated more than 99% relative densities,higher than the value reported by Markforged Inc.(~96%).Based on parallel porosities observed in the computed tomography results,it can be suggested that by modifying the infill pattern during printing,it would be possible to increase the final relative density.The microhardness of the sintered samples in this study was higher than that of the standard sample provided by Markforged Inc.Sintering at 1330℃ for 4 h increased the density of the printed sample without compromising its mechanical properties.According to X-ray diffraction analysis,the standard sample provided by Markforged Inc.and“1330℃—4 h”one had similar stable phases,although copper-rich intermetallics were more abundant in the microstructure of reference samples.This study is expected to facilitate the adoption of indirect metal AM methods by different sectors,thanks to the high achievable relative densities reported here.展开更多
The segregation of Cu and Ni in a 17-4PH stainless steel piston rod has been confirmed to be responsible for the cracking after heat treatment.Further investigation showed that the segregation zone was composed of thr...The segregation of Cu and Ni in a 17-4PH stainless steel piston rod has been confirmed to be responsible for the cracking after heat treatment.Further investigation showed that the segregation zone was composed of three layers,namely the fine grain martensitic layer,the coarse grain martensitic layer and the coarse grain austenitic layer from the matrix to the crack surface.Three button ingots with the same chemical compositions as those three layers have been prepared to evaluate the grain size distribution,microstructure and mechanical properties.The effects of Cu and Ni segregation on the microstructures of those three layers have been explored by thermodynamic calculation.Based on the microstructure and mechanical properties results,an intensive understanding of the cracking in the segregation zone was therefore reached.展开更多
The effect of aging temperature on erosion corrosion （E-C） behavior of 17-4PH stainless steels in dilute sulphuric acid slurry containing solid particles was studied by using self-made rotating E-C apparatus. The ef...The effect of aging temperature on erosion corrosion （E-C） behavior of 17-4PH stainless steels in dilute sulphuric acid slurry containing solid particles was studied by using self-made rotating E-C apparatus. The effect of impact velocity on EC behavior of 17 4PH steels at different aging temperatures was analyzed. Surface micrographs of the specimens after E C test were observed by using scanning electron microscope （SEM）. The results showed that under the condition of the same solution heat treatment, when aging temperature ranged from 400 ℃ to 610℃, the hardness reached the highest value near the temperature 460℃. The characteristics of E-C for 17-4PH stainless steels at different aging temperatures were as follows： pure erosion （wear） was dominant, corrosion was subordinate and at the same time corrosion promoted erosion. The effect of aging temperature on E-C rate of 17-4PH steels was not significant at low impact velocity, but it was found that E-C resistance of 17-4PH steels aged near 460℃ was the most excellent due to the best precipitation strengthening effect of fine and dispersed e-Cu phase. With a prerequisite of appropriate corrosion resistance, the precipitation hardening could significantly improve the E-C resistance of the materials.展开更多
The feedstock based on the binder 65%PW-30%EVA-5%SA has the best general rheological properties for the 17-4PH stainless steel powder. The 17-4PH stainless steel compacts sintered at 1 380 ℃ for 90 min have the best ...The feedstock based on the binder 65%PW-30%EVA-5%SA has the best general rheological properties for the 17-4PH stainless steel powder. The 17-4PH stainless steel compacts sintered at 1 380 ℃ for 90 min have the best mechanical properties and the good microstructure with homogeneously distributed pore structure and the moderate-sized grains. Whereas the compacts sintered for 60 min and 120 min show an inadequate and an over-sintered microstructure respectively. The compacts sintered at 1380 ℃ for 90 min have the density of 7.70 g/cm^3, the strength of 1 275 MPa, the elongation of 5%, and hardness of HRC36. With the increase of sintering temperature, the density, strength and hardness increase, while the elongation decreases. The 17-4PH stainless steel has good corrosion resistance, showing an activation-passivation polarization curve. But the passivation potential range is narrow and the spot corrosion potential is low, indicating a low anti-spot corrosive properties.展开更多
17-4 precipitation-hardened(PH)stainless steel(SS)exhibits high strength and good corrosion resistance via Cu-precipitation hardening.Unlike conventional wrought 17-4PH SS,Cu segregation andε-Cu pre-cipitates are obs...17-4 precipitation-hardened(PH)stainless steel(SS)exhibits high strength and good corrosion resistance via Cu-precipitation hardening.Unlike conventional wrought 17-4PH SS,Cu segregation andε-Cu pre-cipitates are observed in additively manufactured(AM)17-4PH SS owing to the repeated rapid cooling after heating,which characterizes the AM process.In this study,solution treatment was conducted under various temperatures(1,000,1,050,1,100,and 1,200℃)and durations(1,2,4,and 8 h)to minimize the negative effects of Cu segregation andε-Cu precipitates on precipitation hardening.The mechanical prop-erties and microstructures of each condition for the Cu precipitation behavior were examined.Although theε-Cu precipitates did not disappear after solution treatment,the average diameter of theε-Cu precipi-tates tended to decrease with increasing solution treatment temperature and duration.Therefore,solution treatment at a temperature of 1,200℃ for 8 h was the best,resulting in improved strength compared to the conventional solution treatment at 1,050℃.Solution treatment on at least 1,100℃ is effective in AM.展开更多
Different from previous attention on the austenization temperature or dwelling time of PH13-8Mo stainless steels,the effect of the cooling rate on the hierarchical microstructure and mechanical properties was revealed...Different from previous attention on the austenization temperature or dwelling time of PH13-8Mo stainless steels,the effect of the cooling rate on the hierarchical microstructure and mechanical properties was revealed.For all of water,oil,air and furnace cooling,there is almost-complete martensite with the favorable hardenability.The increase in cooling rate mainly increases the density of dislocation and residual strain in the as-solution annealed matrix.After aging treatment,the cooling rate dominates the ratio of high-angle grain boundaries(HAGBs)instead of the size of martensite blocks.The ratio of HAGBs continuously increases with the decreased cooling rate,while the width of blocks maintains 2.40-2.49μm.Meanwhile,more reversed austenite distributes at the martensite sub-grain boundaries.By comparison,the increased rate of water cooling contributes to a favorable precipitation of NiAl with fine size and dispersive distribution caused by more accumulated internal defects of vacancies and dislocations.With the decrease of cooling rate,NiAl precipitates exhibits a similar diameter of~7 nm while a larger inter-particle distance of~22 nm.In the case of low cooling rate(oil,air and furnace),the stable precipitation strengthening effect contributes to a high yield strength of~1.3 GPa and ultimate tensile strength of~1.4 GPa.The high-ratio HAGBs,reversed austenite and NiAl precipitates with larger-interparticle distance synergistically improve the impact toughness(V-notched Charpy impact energy of 100-110 J).展开更多
金属材料挤出成型(metal material extrusion, MME)是采用金属粉末与聚合物黏结剂混合丝材为原料,通过成型、脱脂和烧结工艺(shaping-debinding-sintering, S-D-S)制造纯金属零部件的一种增材制造技术。随着MME技术的发展,亟须对其制品...金属材料挤出成型(metal material extrusion, MME)是采用金属粉末与聚合物黏结剂混合丝材为原料,通过成型、脱脂和烧结工艺(shaping-debinding-sintering, S-D-S)制造纯金属零部件的一种增材制造技术。随着MME技术的发展,亟须对其制品的抗冲击性能进行研究,然而相关信息非常匮乏。制备了不同过程参数下的MME试件,并采用夏比摆锤冲击试验研究了其抗冲击性能,探讨了成型方向、填充角度、挤出温度、床温及成型速度等过程参数对试件冲击吸收功的影响。结果表明:当填充角度为45°时,侧置方向成型试件的抗冲击性能最佳,水平方向次之,竖直方向最差;而在0°填充角度下,水平方向成型试件性能最好;进一步提高挤出温度、床温并降低成型速度,可以显著增强试件的抗冲击性能。研究结果为优化MME成型参数提供了理论依据,拓展了其在承受冲击载荷场景下的应用潜力。展开更多
The effects of atmosphere conditions on microstructural and mechanical properties of stainless steel 17-4PH components fabricated by laser direct manufacturing (LDM) were investigated through mea-surements on phase co...The effects of atmosphere conditions on microstructural and mechanical properties of stainless steel 17-4PH components fabricated by laser direct manufacturing (LDM) were investigated through mea-surements on phase constitution, porosity, tensile strength, fracture morphology, hardness and evolution of substrate temperature. Results showed that the samples produced in air atmosphere condition pos-sessed higher tensile strength and hardness for both as-deposited and heat-treated states than that in Ar chamber condition, due to dispersion strengthening effect of amorphous oxide particles and nitrogen solution strengthening as a result of higher content of oxygen and nitrogen. The temperature of substrate heat accumulation was higher in Ar chamber condition, leading to dramatically lower porosity and more reverse austenite, which also contributed to the lower strength and hardness.展开更多
The relationship between the microstructure transformation of type 17-4 PH stainless steel and the aging hardening behavior was investigated. The results showed that, when 17-4 PH stainless steel aging at 595℃, the b...The relationship between the microstructure transformation of type 17-4 PH stainless steel and the aging hardening behavior was investigated. The results showed that, when 17-4 PH stainless steel aging at 595℃, the bulk hardness of samples attains its peak value （42.5 HRC） for about 20 min, and then decreases at all time. TEM revealed the microstructure corresponding with peak hardness is that the fine spheroid-shape copper with the fcc crystal structure and the fiber-shape secondary carbide M23C6 precipitated from the lath martensite matrix. Both precipitations of copper and M23C6 are the reasons for strengthening of the alloy at this temperature. With the extension of holding time at this temperature, the copper and secondary carbide grow and lose the coherent relationship with the matrix, so the bulk hardness of samples decreases.展开更多
Additive Manufacturing (AM) of metals allows the production of parts with complex designs, offeringadvanced properties if the evolution of the texture can be controlled. 17-4 precipitation hardening (PH)stainless stee...Additive Manufacturing (AM) of metals allows the production of parts with complex designs, offeringadvanced properties if the evolution of the texture can be controlled. 17-4 precipitation hardening (PH)stainless steel is a high strength, high corrosion resistance alloy used in a range of industries suitable forAM, such as aerospace and marine. Despite 17-4 PH being one of the most common steels for AM, thereare still gaps in the understanding of its AM processing–structure relationships. These include the natureof the matrix phase, as well as the development of texture through AM builds under different processingconditions. We have investigated how changing the laser power and scanning strategy affects the microstructure of 17-4 PH during laser powder bed fusion. It is revealed that the matrix phase is δ-ferritewith a limited austenite presence, mainly in regions of the microstructure immediately below melt pools.Austenite fraction is independent of the printing pattern and laser power. However, reducing the timebetween adjacent laser passes during printing results in an increase in the austenite volume fraction.Another effect of the higher laser power, as well as additional remelting within the printing strategy, isan increase in the average grain size by epitaxial ferrite grain growth across multiple build layers andthe development of a mosaic type microstructure. Changes to the scanning strategy have significant impacts on the textures observed along the build direction, while (100) texture along the scanning directionis observed consistently. Mechanisms for texture formation and the mosaic structure are proposed thatpresents a pathway to the design of texture via AM process control.展开更多
17-4 precipitation hardening(PH)stainless steel is a multi-purpose engineering alloy offering an excellent trade-off between strength,toughness,and corrosion properties.It is commonly employed in additive manufacturin...17-4 precipitation hardening(PH)stainless steel is a multi-purpose engineering alloy offering an excellent trade-off between strength,toughness,and corrosion properties.It is commonly employed in additive manufacturing via laser powder bed fusion owing to its good weldability.However,there are remaining gaps in the processing-structure-property relationships for AM 17-4 PH that need to be addressed.For instance,discrepancies in literature regarding the as-built microstructure,subsequent development of the matrix phase upon heat treatment,as well as the as-built residual stress should be addressed to enable reproducible printing of 17-4 builds with superior properties.As such,this work applies a comprehensive characterisation and testing approach to 17-4 PH builds fabricated with different processing parameters,both in the as-built state and after standard heat treatments.Tensile properties in as-built samples both along and normal to the build direction were benchmarked against standard wrought samples in the solution annealed and quenched condition(CA).When testing along the build direction,higher ductility was observed for samples produced with a higher laser power(energy density)due to the promotion of interlayer cohesion and,hence,reduction of interlayer defects.Following the CA heat treatment,the austenite volume fraction increased to∼35%,resulting in a lower yield stress and greater work hardening capacity than the as-built specimens due to the transformation induced plasticity effect.Neutron diffraction revealed a slight reduction in the magnitude of residual stress with laser power.A concentric scanning strategy led to a higher magnitude of residual stress than a bidirectional raster pattern.展开更多
The effect of aging temperature on stress corrosion crocking of 17-4 precipitation-hardened(PH)stainless steel in simulated stimulant oil well environment was studied by the method B-NACE standard bent-beam test.It is...The effect of aging temperature on stress corrosion crocking of 17-4 precipitation-hardened(PH)stainless steel in simulated stimulant oil well environment was studied by the method B-NACE standard bent-beam test.It is found that when aging temperature ranges from 480 to 610℃,the sensitivity of hydrogen embrittlement decreases significantly.展开更多
对于17-4PH钢超大型锻件而言,其成分宏观偏析、缩孔疏松、碳化物析出、裂纹的产生以及晶粒度的大小通常难以控制,从而严重影响其力学性能和后续的产品使用。以28 t 17-4PH钢电渣锭从生产至获得成品的生产为例,从对重熔渣系设计、锻造工...对于17-4PH钢超大型锻件而言,其成分宏观偏析、缩孔疏松、碳化物析出、裂纹的产生以及晶粒度的大小通常难以控制,从而严重影响其力学性能和后续的产品使用。以28 t 17-4PH钢电渣锭从生产至获得成品的生产为例,从对重熔渣系设计、锻造工艺流程以及固溶时效热处理等重点工艺入手,优化了产品制造过程,特别通过精确控制固溶和时效工艺,在350~1050℃范围内分步加热保温固溶处理以及150~530℃范围内多次加热保温时效处理,成功控制了产品中残余奥氏体、富铜相及弥散析出相的体积分数,达到了可控的基体晶粒度,有效抑制了不利相的析出,同时显著降低了工件的内部应力及开裂风险。通过优化措施不仅保证了产品的力学性能,而且显著延长了其使用寿命,有效解决了该领域中的多项技术难题。展开更多
文摘Indirect additive manufacturing(AM)methods have recently attracted attention from researchers thanks to their great potential for cheap,straightforward,and small-scale production of metallic components.Atomic diffusion additive manufacturing(ADAM),a variant of indirect AM methods,is a layer-wise indirect AM process recently developed based on fused deposition modeling and metal injection molding.However,there is still limited knowledge of the process conditions and material properties fabricated through this process,where sintering plays a crucial role in the final consolidation of parts.Therefore,this research,for the first time,systematically investigates the impact of various sintering conditions on the shrinkage,relative density,microstructure,and hardness of the 17-4PH ADAM samples.For this reason,as-washed samples were sintered under different time-temperature combinations.The sample density was evaluated using Archimedes,computed tomography,and image analysis methods.The outcomes revealed that sintering variables significantly impacted the density of brown 17-4PH Stainless Steel samples.The results indicated more than 99% relative densities,higher than the value reported by Markforged Inc.(~96%).Based on parallel porosities observed in the computed tomography results,it can be suggested that by modifying the infill pattern during printing,it would be possible to increase the final relative density.The microhardness of the sintered samples in this study was higher than that of the standard sample provided by Markforged Inc.Sintering at 1330℃ for 4 h increased the density of the printed sample without compromising its mechanical properties.According to X-ray diffraction analysis,the standard sample provided by Markforged Inc.and“1330℃—4 h”one had similar stable phases,although copper-rich intermetallics were more abundant in the microstructure of reference samples.This study is expected to facilitate the adoption of indirect metal AM methods by different sectors,thanks to the high achievable relative densities reported here.
基金financially sponsored by National Natural Science Foundation of China(Grant No.51201160)Youth Innovation Promotion Association of Chinese Academy of Sciences(2017233)Science and Technology Innovation Foundation from Institute of Metal Research,Chinese Academy of Sciences(Grant No.2015-ZD04)
文摘The segregation of Cu and Ni in a 17-4PH stainless steel piston rod has been confirmed to be responsible for the cracking after heat treatment.Further investigation showed that the segregation zone was composed of three layers,namely the fine grain martensitic layer,the coarse grain martensitic layer and the coarse grain austenitic layer from the matrix to the crack surface.Three button ingots with the same chemical compositions as those three layers have been prepared to evaluate the grain size distribution,microstructure and mechanical properties.The effects of Cu and Ni segregation on the microstructures of those three layers have been explored by thermodynamic calculation.Based on the microstructure and mechanical properties results,an intensive understanding of the cracking in the segregation zone was therefore reached.
文摘The effect of aging temperature on erosion corrosion （E-C） behavior of 17-4PH stainless steels in dilute sulphuric acid slurry containing solid particles was studied by using self-made rotating E-C apparatus. The effect of impact velocity on EC behavior of 17 4PH steels at different aging temperatures was analyzed. Surface micrographs of the specimens after E C test were observed by using scanning electron microscope （SEM）. The results showed that under the condition of the same solution heat treatment, when aging temperature ranged from 400 ℃ to 610℃, the hardness reached the highest value near the temperature 460℃. The characteristics of E-C for 17-4PH stainless steels at different aging temperatures were as follows： pure erosion （wear） was dominant, corrosion was subordinate and at the same time corrosion promoted erosion. The effect of aging temperature on E-C rate of 17-4PH steels was not significant at low impact velocity, but it was found that E-C resistance of 17-4PH steels aged near 460℃ was the most excellent due to the best precipitation strengthening effect of fine and dispersed e-Cu phase. With a prerequisite of appropriate corrosion resistance, the precipitation hardening could significantly improve the E-C resistance of the materials.
文摘The feedstock based on the binder 65%PW-30%EVA-5%SA has the best general rheological properties for the 17-4PH stainless steel powder. The 17-4PH stainless steel compacts sintered at 1 380 ℃ for 90 min have the best mechanical properties and the good microstructure with homogeneously distributed pore structure and the moderate-sized grains. Whereas the compacts sintered for 60 min and 120 min show an inadequate and an over-sintered microstructure respectively. The compacts sintered at 1380 ℃ for 90 min have the density of 7.70 g/cm^3, the strength of 1 275 MPa, the elongation of 5%, and hardness of HRC36. With the increase of sintering temperature, the density, strength and hardness increase, while the elongation decreases. The 17-4PH stainless steel has good corrosion resistance, showing an activation-passivation polarization curve. But the passivation potential range is narrow and the spot corrosion potential is low, indicating a low anti-spot corrosive properties.
基金This work was funded by Yangyoung Foundation and supported by the Technology Innovation Program(grant No.20009815,Development of DfAM-based 3D printing technology for lightweight and integrated aerospace parts)funded by the Ministry of Trade,Industry&Energy(MOTIE,Korea).
文摘17-4 precipitation-hardened(PH)stainless steel(SS)exhibits high strength and good corrosion resistance via Cu-precipitation hardening.Unlike conventional wrought 17-4PH SS,Cu segregation andε-Cu pre-cipitates are observed in additively manufactured(AM)17-4PH SS owing to the repeated rapid cooling after heating,which characterizes the AM process.In this study,solution treatment was conducted under various temperatures(1,000,1,050,1,100,and 1,200℃)and durations(1,2,4,and 8 h)to minimize the negative effects of Cu segregation andε-Cu precipitates on precipitation hardening.The mechanical prop-erties and microstructures of each condition for the Cu precipitation behavior were examined.Although theε-Cu precipitates did not disappear after solution treatment,the average diameter of theε-Cu precipi-tates tended to decrease with increasing solution treatment temperature and duration.Therefore,solution treatment at a temperature of 1,200℃ for 8 h was the best,resulting in improved strength compared to the conventional solution treatment at 1,050℃.Solution treatment on at least 1,100℃ is effective in AM.
基金supported by the National Key Research and Development Program(Grant No.2024YFB3714200)the National Natural Science Foundation of China(Grant Nos.52173305,52233017,52203384,U244120568 and U2441261)+1 种基金the Key Program of the Chinese Academy of Sciences(Grant No.RCJJ-145-24-40)LingChuang Research Project of China National Nuclear Corporation,and Special Funds for Science and Technology Planning of Jiangsu Province(No.BZ2024059).
文摘Different from previous attention on the austenization temperature or dwelling time of PH13-8Mo stainless steels,the effect of the cooling rate on the hierarchical microstructure and mechanical properties was revealed.For all of water,oil,air and furnace cooling,there is almost-complete martensite with the favorable hardenability.The increase in cooling rate mainly increases the density of dislocation and residual strain in the as-solution annealed matrix.After aging treatment,the cooling rate dominates the ratio of high-angle grain boundaries(HAGBs)instead of the size of martensite blocks.The ratio of HAGBs continuously increases with the decreased cooling rate,while the width of blocks maintains 2.40-2.49μm.Meanwhile,more reversed austenite distributes at the martensite sub-grain boundaries.By comparison,the increased rate of water cooling contributes to a favorable precipitation of NiAl with fine size and dispersive distribution caused by more accumulated internal defects of vacancies and dislocations.With the decrease of cooling rate,NiAl precipitates exhibits a similar diameter of~7 nm while a larger inter-particle distance of~22 nm.In the case of low cooling rate(oil,air and furnace),the stable precipitation strengthening effect contributes to a high yield strength of~1.3 GPa and ultimate tensile strength of~1.4 GPa.The high-ratio HAGBs,reversed austenite and NiAl precipitates with larger-interparticle distance synergistically improve the impact toughness(V-notched Charpy impact energy of 100-110 J).
文摘金属材料挤出成型(metal material extrusion, MME)是采用金属粉末与聚合物黏结剂混合丝材为原料,通过成型、脱脂和烧结工艺(shaping-debinding-sintering, S-D-S)制造纯金属零部件的一种增材制造技术。随着MME技术的发展,亟须对其制品的抗冲击性能进行研究,然而相关信息非常匮乏。制备了不同过程参数下的MME试件,并采用夏比摆锤冲击试验研究了其抗冲击性能,探讨了成型方向、填充角度、挤出温度、床温及成型速度等过程参数对试件冲击吸收功的影响。结果表明:当填充角度为45°时,侧置方向成型试件的抗冲击性能最佳,水平方向次之,竖直方向最差;而在0°填充角度下,水平方向成型试件性能最好;进一步提高挤出温度、床温并降低成型速度,可以显著增强试件的抗冲击性能。研究结果为优化MME成型参数提供了理论依据,拓展了其在承受冲击载荷场景下的应用潜力。
基金financial support from National Key Research and Development Program of China [grant number 2016YFB1100203]Key Research and Development Program of Jiangxi Province [grant numbers 20171BBE50022, 20151BBE51065]+1 种基金Scientific Research Special Funds of Jiangxi Academy of Sciences [grant numbers 2014-XTPH1-16, 2014-YYB16]Key Research Project of Jiangxi Academy of Sciences [grant number 2016-YZD2-01]
文摘The effects of atmosphere conditions on microstructural and mechanical properties of stainless steel 17-4PH components fabricated by laser direct manufacturing (LDM) were investigated through mea-surements on phase constitution, porosity, tensile strength, fracture morphology, hardness and evolution of substrate temperature. Results showed that the samples produced in air atmosphere condition pos-sessed higher tensile strength and hardness for both as-deposited and heat-treated states than that in Ar chamber condition, due to dispersion strengthening effect of amorphous oxide particles and nitrogen solution strengthening as a result of higher content of oxygen and nitrogen. The temperature of substrate heat accumulation was higher in Ar chamber condition, leading to dramatically lower porosity and more reverse austenite, which also contributed to the lower strength and hardness.
基金This work was financially supported by the Key Nuclear Fuel and Nuclear Materials Laboratory of China(No.51481080104ZS8501).
文摘The relationship between the microstructure transformation of type 17-4 PH stainless steel and the aging hardening behavior was investigated. The results showed that, when 17-4 PH stainless steel aging at 595℃, the bulk hardness of samples attains its peak value （42.5 HRC） for about 20 min, and then decreases at all time. TEM revealed the microstructure corresponding with peak hardness is that the fine spheroid-shape copper with the fcc crystal structure and the fiber-shape secondary carbide M23C6 precipitated from the lath martensite matrix. Both precipitations of copper and M23C6 are the reasons for strengthening of the alloy at this temperature. With the extension of holding time at this temperature, the copper and secondary carbide grow and lose the coherent relationship with the matrix, so the bulk hardness of samples decreases.
基金supported under the Australian Research Council’s DECRA (project number DE180100440)the UNSW Scientia Fellowship schemes
文摘Additive Manufacturing (AM) of metals allows the production of parts with complex designs, offeringadvanced properties if the evolution of the texture can be controlled. 17-4 precipitation hardening (PH)stainless steel is a high strength, high corrosion resistance alloy used in a range of industries suitable forAM, such as aerospace and marine. Despite 17-4 PH being one of the most common steels for AM, thereare still gaps in the understanding of its AM processing–structure relationships. These include the natureof the matrix phase, as well as the development of texture through AM builds under different processingconditions. We have investigated how changing the laser power and scanning strategy affects the microstructure of 17-4 PH during laser powder bed fusion. It is revealed that the matrix phase is δ-ferritewith a limited austenite presence, mainly in regions of the microstructure immediately below melt pools.Austenite fraction is independent of the printing pattern and laser power. However, reducing the timebetween adjacent laser passes during printing results in an increase in the austenite volume fraction.Another effect of the higher laser power, as well as additional remelting within the printing strategy, isan increase in the average grain size by epitaxial ferrite grain growth across multiple build layers andthe development of a mosaic type microstructure. Changes to the scanning strategy have significant impacts on the textures observed along the build direction, while (100) texture along the scanning directionis observed consistently. Mechanisms for texture formation and the mosaic structure are proposed thatpresents a pathway to the design of texture via AM process control.
基金Funding by the AUSMURI program,Department of Industry,In-novation and Science,Australia is acknowledged.
文摘17-4 precipitation hardening(PH)stainless steel is a multi-purpose engineering alloy offering an excellent trade-off between strength,toughness,and corrosion properties.It is commonly employed in additive manufacturing via laser powder bed fusion owing to its good weldability.However,there are remaining gaps in the processing-structure-property relationships for AM 17-4 PH that need to be addressed.For instance,discrepancies in literature regarding the as-built microstructure,subsequent development of the matrix phase upon heat treatment,as well as the as-built residual stress should be addressed to enable reproducible printing of 17-4 builds with superior properties.As such,this work applies a comprehensive characterisation and testing approach to 17-4 PH builds fabricated with different processing parameters,both in the as-built state and after standard heat treatments.Tensile properties in as-built samples both along and normal to the build direction were benchmarked against standard wrought samples in the solution annealed and quenched condition(CA).When testing along the build direction,higher ductility was observed for samples produced with a higher laser power(energy density)due to the promotion of interlayer cohesion and,hence,reduction of interlayer defects.Following the CA heat treatment,the austenite volume fraction increased to∼35%,resulting in a lower yield stress and greater work hardening capacity than the as-built specimens due to the transformation induced plasticity effect.Neutron diffraction revealed a slight reduction in the magnitude of residual stress with laser power.A concentric scanning strategy led to a higher magnitude of residual stress than a bidirectional raster pattern.
文摘The effect of aging temperature on stress corrosion crocking of 17-4 precipitation-hardened(PH)stainless steel in simulated stimulant oil well environment was studied by the method B-NACE standard bent-beam test.It is found that when aging temperature ranges from 480 to 610℃,the sensitivity of hydrogen embrittlement decreases significantly.
文摘对于17-4PH钢超大型锻件而言,其成分宏观偏析、缩孔疏松、碳化物析出、裂纹的产生以及晶粒度的大小通常难以控制,从而严重影响其力学性能和后续的产品使用。以28 t 17-4PH钢电渣锭从生产至获得成品的生产为例,从对重熔渣系设计、锻造工艺流程以及固溶时效热处理等重点工艺入手,优化了产品制造过程,特别通过精确控制固溶和时效工艺,在350~1050℃范围内分步加热保温固溶处理以及150~530℃范围内多次加热保温时效处理,成功控制了产品中残余奥氏体、富铜相及弥散析出相的体积分数,达到了可控的基体晶粒度,有效抑制了不利相的析出,同时显著降低了工件的内部应力及开裂风险。通过优化措施不仅保证了产品的力学性能,而且显著延长了其使用寿命,有效解决了该领域中的多项技术难题。
